On Windows 7 Ultimate x64.
Of course, it's intermittent, so it's difficult to provide an absolute repro, but it occurs sometimes by doing the following:
Open multiple files. Use one to create another vertical tab group, so you have two vertical tab groups. Note which tab group is active. Right click on an inactive file in the inactive tab group, note that it does not always become the active tab. Sometimes the active tab before the right-click remains active, and the context menu is appropriate to that tab.
